1. Field of the Invention
The present invention relates to a recording medium, near field optical head, and optical recording device capable of utilizing near field light to record and reproduce information in a highly precise manner, and a manufacturing method thereof.
2. Description of Related Art
Typically, Scanning Probe Microscopes (SPMs) are used in Scanning Tunnel Microscopes (STMs) and Atomic Force Microscopes (AFMs) for monitoring microscopic regions in the order of a few nanometers of a sample surface. An SPM monitors a sample surface with a probe having a pointed tip. Mutual interaction of tunnel currents and interatomic forces occurring between the probe and the sample surface are then taken as subjects of monitoring and an image of a resolution depending upon the shape of the probe tip can be obtained. This does, however, place relatively severe constraints on the sample being monitored.
Near field optical microscopes where the subject of the monitoring is taken to be the mutual interaction occurring between the near field light generated at the sample surface and the probe so that it is possible to monitor microscopic regions of the sample surface have recently come to the forefront.
With these near field optical microscopes, propagating light illuminates the surface of the sample so as to generate near field light. Near field light generated in this manner is then scattered by a probe with a pointed tip and this scattered light is processed in the same manner as the detection of propagated light in the related art. This eliminates the boundaries in monitoring resolution of related optical microscopes and enables observation of even more microscopic regions. The observation of the optical properties of the sample occurring at microscopic regions can therefore by achieved by sweeping the wavelength of the light the sample surface is illuminated with.
In addition to utilization as a microscope, applications are also possible in high-density optical memory recording where near field light of a high energy density is generated at a microscopic opening of the optical fiber probe by introducing light of relatively substantial intensity to the sample via the optical fiber probe so as to cause the structure or the physical properties of the sample surface to be changed in a localized manner by this near field light.
Cantilever optical probes as disclosed, for example, in U.S. Pat. No. 5,294,790 where an opening passing through a silicon substrate is formed using semiconductor manufacturing technology such as photolithography etc., an insulation film is formed on one side of the silicon substrate, and a conical optical waveguide layer is formed on the insulation film on the opposite side to the opening have also been put forward as probes for use in near-field optical microscopes. With this kind of cantilever-type optical probe, an optical fiber is inserted into the opening, and light is made to pass through a microscopic opening formed by coating everything but the tip of the optical waveguide layer with a metal film.
The use of flat probes that do not have pointed tips as the aforementioned probes do has also been proposed. This plane probe is formed with an opening having a conical structure, by anisotropic etching of a silicon substrate, with a vertex that is a few tens of nanometers across which can be passed through. Making a plurality of plane probes of this structure on the same substrate using semiconductor manufacturing technology, i.e. making an array of plane probes, is straightforward and utilization in optical memory heads for reproducing and recording optical memory using near field light is possible. Flying heads as used in related hard discs and having plane probes have also been put forward as optical heads employing this plane probe. Such flying heads are designed such that aerodynamic force causes the heads to float 50 to 100 nanometers from the recording medium. A microscopic opening is formed in the recording medium side of the flying head and near field light is generated so as to perform optical recording and reproduction.
A schematic view of a near field optical information recording/reproduction device employing this kind of flying head is shown in FIG. 1. Here, a near field optical head 5 is fitted to the end of a suspension arm 10. The near field optical head 5 scans the surface of the recording medium 1 while floating a few tens of nanometers from the surface of the recording medium 1 due to air-pressure received from a disc recording medium 1 rotating at high-speed. At the near field optical head 5, light from the laser light source (omitted from the drawings) is focused at the lens so as to be made incident. The surface of the recording medium 1 and the near field optical head 5 mutually interact via the near field light so that scattered light generated as a result is taken as an output signal detected by an optical sensing element (not shown in the drawings).
However, because this kind of optical memory utilizes near field light, ultra-high density optical memory below the optical diffraction limit can be realized but unfortunately, on the other hand, the efficiency with which light can be utilized is lowered, and very little light is received by the light-receiving element.
In order to resolve this problem, in the related art, the intensity of the laser light employed is made strong or the conical structure of the plane probe constituting the near field light head is filled with a ball lens etc.
However, when the intensity of the laser light is increased, new problems with regards to heat generated and power consumed occur. Further, when a ball lens is employed, it is necessary to align the position of the ball lens which causes costs to increase. This has the result that it is difficult to adjust the focal point of, light at an opening for all the near field optical heads during large-scale production due to variations in the individual ball lenses.
It is therefore also difficult to bring about ultra-high density memory utilizing near field light while maintaining low power consumption and mass production at a low price.
In order to resolve the problems of the method of the related art while increasing the efficiency with which light is utilized, it is the object of the present invention to implement a structure utilizing a plasmon mechanism where optical energy is temporarily converted into plasmon energy of a metal particulate and is then converted back to being optical energy after passing through a microscopic region.